Most wood adhesives used today are based on urea formaldehyde resins which are not considered to have acceptable weatherability. Although melamine resins are increasingly used to meet higher requirements for bond strength and moisture resistance, they are not deemed suitable for preparing weatherproof adhesive joints. Weatherproof wood joints have been produced only with phenolic resins capable of alkaline cure, however, such joints are dark in color and such phenolic resins can damage wood under conditions of cure.
Since urea is economically inexpensive compared to melamine, it is desirable to use as much urea as possible and as little of melamine as possible, however, it is well known that use of urea in wood adhesives results in poor weatherability and poor durability of bonds formed with such adhesives. It has been unexpectedly discovered that, when condensed in a proper sequence, adhesives containing condensed urea will be stable and will provide excellent weatherability to bonds formed thereby.